1. Field of the Invention
This invention concerns transmission mechanisms for automotive vehicles, and more particularly relates to a control apparatus for a continuously variable speed ratio transmission.
2. Description of the Prior Art
Continuously variable transmission (CVT) devices employing movable-sheave pulleys with variable pitch diameters are in widespread use in recreational vehicles, golf carts, go-carts, mini-bikes and snowmobiles.
The CVT with variable pitch pulleys is described below, and this description will be best understood when read in conjunction with the following drawings in which:
FIG. 11A is a top view of a speed-sensitive CVT at low speed.
FIG. 11B is a top view of a speed-sensitive CVT at high speed.
FIG. 11C is a top view of a torque-sensitive type CVT at low speed.
FIG. 11D is a top view of a torque-sensitive type CVT at high speed.
FIG. 11E is a top view of a torque-sensitive type CVT at medium output speed.
FIG. 11F is a sectional view along line 11Fxe2x80x9411F of FIG. 11A.
FIG. 11G is a sectional view along line 11Gxe2x80x9411G of FIG. 11.
FIG. 11H is a sectional view along line Z-Zxe2x80x2 of FIG. 11E.
Referring now to the above drawings wherein similar letters refer to similar parts, there is shown a driver pulley F and a driven pulley G interconnected by a xe2x80x9cVxe2x80x9d type belt H. Driver pulley F is fixedly mounted on the engine output shaft I, and is comprised of stationary sheave J and axially movable sheave K. Associated with sheave K is a bowl-shaped ramp plate L which houses centrifugally actuated roller weights M. When the engine speed increases, the roller weights M follow the contour of ramp plate L and force movable sheave K toward stationary sheave J. Such action moves V-belt H toward the outer circumference of drive pulley F, further causing the belt to pull against driven pulley G.
Driven pulley G is fixedly mounted on output shaft N, and has a stationary sheave P and axially movable sheave Q. The movable sheave Q is normally constantly pressed against the stationary sheave P by the action of a spring R and/or a cam actuator S. When equipped with spring R, pulley G is speed sensitive. When equipped with cam actuator S, pulley G is torque sensitive.
When the engine is at xe2x80x9cidlexe2x80x9d, or running below a preset xe2x80x9cengagement speedxe2x80x9d, the movable sheave K of driver pulley F rests at its farthest point from stationary sheave J, and does not apply pressure on the belt. In such condition, no power is transmitted to driven pulley G, and the system remains disengaged, namely at xe2x80x9cneutralxe2x80x9d. As the engine speed increases beyond the xe2x80x9cengagement speedxe2x80x9d, the centrifugally actuated roller weights M follow the inner contour of bowl-shaped ramp plate L, forcing movable sheave K towards stationary sheave J, thereby exerting axial displacement force against the belt. Initially, as the belt is engaged, it rides close to the center of driver pulley F and it also rides at the outer edge of driven pulley G, as shown in FIG. 11A. The driver pulley F, therefore, carries the belt at a smaller pitch diameter while the driven pulley G carries the belt at a correspondingly larger pitch diameter by virtue of the action of the driven pulley spring R and/or cam actuator S. This creates a xe2x80x9clow gearxe2x80x9d ratio condition.
As the rotational speed of output shaft I increases, roller weights M move further centrifugally on ramp plate L, forcing movable sheave K against belt H which is then forced farther toward the outer edge of driver pulley F. This causes the belt to force itself deeper into the inner portion of drive pulley G as it forces driven pulley movable sheave Q farther from driven pulley stationary sheave P and compresses spring R. This creates a xe2x80x9chigh gearxe2x80x9d ratio condition, as shown in FIG. 11B If the driven pulley G is equipped with a cam actuator S, when increased load occurs (such as on climbing a hill) after the vehicle is up to speed, the cam actuator takes over and automatically xe2x80x9cdownshiftxe2x80x9d without loss of engine speed, as shown in FIG. 11E.
It is accordingly seen that the CVT mechanism is infinitely variable between the low gear position shown in FIGS. 11A and 11C and high gear positions shown in FIGS. 11B and 11D. Furthermore, the torque-sensitive type system automatically and continuously adjusts for variations in load as well.
The CVT automatic transmission is relatively inexpensive, and has found wide application in recreational vehicles, snowmobiles, lawn mowers, go-karts, golf carts, and similar vehicles. However, its use in automotive vehicles has been limited by its relatively narrow range of speed reduction ratios generally no greater than from 3:1 for xe2x80x9clowxe2x80x9d through 1:0.81 for xe2x80x9chighxe2x80x9d. This has not been adequate for cars and trucks, which require not only greater low speed torque for satisfactory acceleration, but also much higher top speeds for highway travel. Furthermore, the CVT mechanism does not readily accommodate reverse motion and parking brake functionality.
Efforts to extend the operational range of the CVT have been varied, most being through the addition of complex and expensive machinery which tends to nullify any cost advantage over conventional automatic transmissions which use hydraulic torque converters. Typical prior efforts are described in the following patent references.
U.S. Pat. No. 5,971,887 discloses infinitely variable ratio pulleys similar to the CVT described above and adds a planetary gear system associated with the output shaft, complete with the necessary hydraulic pumps, valves, pump and valve control means, brakes and clutches required for the proper functioning of a planetary gear system, to increase the range of operational speed ratios. Furthermore, instead of having a centrifugally actuated driver pulley and spring or cam actuated driven pulley, this invention uses a hydraulic system with associated sensors and control means to actuate the movable sheaves of both pulleys. These features make this transmission too complex and expensive for use in inexpensive light weight vehicles.
U.S. Pat. No. 5,931,760 describes a dual mode CVT having two sets of hydraulically controlled planetary reduction gears to extend the operating range of the system. Additionally, it places a bladed hydrokinetic torque converter unit between the engine and the planetary gearing to provide further torque multiplication for accelerating the vehicle from rest. It also provides means for bypassing the CVT altogether when large starting torque is needed. Again, this system is too complex and expensive for light inexpensive vehicles.
U.S. Pat. No. 5,961,414 describes a dual mode CVT with multiple torque input paths and at least two planetary gearsets, one for reverse and the other(s) for forward drive. Two fixed ratio drive mechanisms provide additional torque pathways with the necessary actuating and control mechanism for coordinating the functioning of the multiple torque input paths.
U.S. Pat. No. 4,990,127 describes a dual range CVT having an added fixed ratio speed mechanism to provide a second power path from the input to output shafts. Two planetary gearsets are employed to extend the torque reduction range of transmission. Multiple plate clutches and a hydraulic system are employed to operate the planetary gear system and move the flanges of the pulleys, with the help of sensors and associated control mechanisms.
U.S. Pat. No. 6,146,308 discloses a transmission having a CVT plus a planetary gear mechanism to extend the operational speed range of the system. Such transmission, as previously stated is expensive because of the necessary system of hydraulic pumps, valves, oil pressure chambers, and associated sensing and control features. Furthermore, the means for applying axial forces to the movable sheaves of the driver and driven pulleys is in the form of oil pressure chambers operated and regulated by hydraulic pumps and valves. This adds even more complexity and cost to the transmission.
U.S. Pat. No. 6,189,412 discloses a CVT wherein the movable sheaves of both the primary and secondary pulleys are hydraulically actuated and controlled. The speed reduction system employs two planetary gear sets, also controlled by hydraulic actuators, clutches, pumps and valves.
It is seen from the above review of the prior art that efforts to extend the range of the transmission drive ratio of the CVT have focused on the addition of planetary reduction gearsets and various other modifications. Such additions substantially increase the complexity and the cost of the transmission, causing it to be impractical for light inexpensive fuel-efficient vehicles.
It is accordingly a primary object of the present invention to provide a modified CVT having an extended range of drive ratios suitable for use in automotive vehicles.
It is a further object of this invention to provide a modified CVT as in the foregoing object having improved mechanical efficiency.
It is another object of the present invention to provide a modified CVT of the aforesaid nature having the added features of reverse motion and parking functionality.
It is a still further object of this invention to provide a modified CVT of the aforesaid nature which is amenable to low cost manufacture and easy maintenance.
It is yet another object of the present invention to provide a modified CVT of the aforesaid nature which can accommodate two different power input sources.
These objects and other objects and advantages of the invention will be apparent from the following description.
The above and other beneficial objects and advantages are accomplished in accordance with the present invention by a control apparatus for a vehicle-mounted CVT having a primary output shaft, said control apparatus comprised of:
a) an enclosure comprised of front, rear and top walls bounded by interior and exterior surfaces,
b) an input shaft of circular cylindrical surface contour adapted to engage said primary output shaft as an axial extension thereof and rotatively journaled to said front and rear walls,
c) low gear and drive gear drive sprocket wheels mounted upon said input shaft in freely rotatable manner and in axially spaced apart relationship, each having, respectively, first and second circular arrays of coupling lobes surrounding said input shaft and axially directed toward said rear wall,
d) axially aligned splines disposed within the surface of said input shaft,
e) a first gear coupler mounted upon said input shaft so as to be rotatively driven thereby and interactive with said splines so as to be axially slidable upon said shaft, and provided with a third circular array of axially directed coupling lobes adapted to engage said first array of lobes,
f) a second gear coupler mounted upon said input shaft so as to be rotatively driven thereby and interactive with said splines so as to be axially slidable upon said shaft, and provided with opposed fourth and fifth circular arrays of axially directed coupling lobes, said fourth array adapted to engage the lobes of said second array,
g) a sixth circular array of coupling lobes fixedly associated with said rear wall and adapted to engage the lobes of said fifth array, thereby preventing rotative movement of said input shaft and creating a parking status of said vehicle,
h) shifting means for sliding said first and second gear couplers along said input shaft,
i) a secondary output shaft journaled to said front and rear walls below said input shaft, and parallel thereto,
j) low gear and drive gear driven sprocket wheels fixedly mounted upon said secondary output shaft, and interactive with said low gear and drive gear drive sprocket wheels by way of positive drive means such as gearing chains, said low gear driven sprocket wheel being of greater diameter than the corresponding low gear drive sprocket wheel, and said drive gear driven sprocket wheel being of substantially equal diameter with the corresponding drive gear drive sprocket wheel,
k) a driven spur gear fixedly mounted upon said secondary output shaft adjacent said rear wall and interactive with a drive spur gear carried by said second gear coupler, said interaction causing said secondary output shaft to rotate oppositely to said output shaft, whereby,
l) shifting movement of said first and second gear couplers produce low speed, high speed or reverse rotational movement of said secondary output shaft, or locked securement thereof.